Safety valves have been used in wells to control them in emergency situations. They typically feature a disc known as a flapper that is biased against a seat above it by a torsion spring mounted on a pivot pin. In many designs a hydraulic system creates pressure at the surface that is transmitted through a control line to a piston in the housing of the valve. The piston is typically coupled to a flow tube for tandem movement. Typically the flow tube and operating piston combination is moved against the bias of a closure spring so that when hydraulic pressure is removed or lost in the control line, the closure spring can move the flow tube and piston back against any net force such as the net hydrostatic pressure in the control line. In some designs the hydrostatic forces in the control line are balanced with a second control line from the surface or a pressurized chamber within the valve housing downhole. When the flow tube moves away from the open flapper, the torsion spring is sufficient to urge the flapper against its seat to keep the well under control.
In wells that are in injection service, such valves are also in use. In injection service the flow is from the surface into the well so as to stimulate production to another well communicating with the same formation. In these applications, flapper valves were used that were controlled by hydraulic control lines from the surface. The present invention addresses ways to hold the valve in the open position while minimizing chatter created by the velocity of the traveling fluid. It also provides for a technique to hold the valve locked open to accommodate through tubing activities further downhole. In so doing the present invention employs forces that can act through the wall of the valve housing without making penetrations into the flow path internal to the housing, one such force being a magnetic force. These and other features of the present invention will be more readily understood from a review of the description of the preferred embodiment and the associated drawings that appear below with the understanding that the claims define the full scope of the invention.
Relevant as background to this invention is U.S. Pat. No. 7,213,653 which deals with use of magnetic force to operate a subsurface safety valve between an open and a closed position.